Twist-beam axle for the rear suspension of a motor vehicle and method for its production

ABSTRACT

The twist-beam axle ( 10 ) comprises a central cross-member ( 11 ) compliant to torsion and a pair of trailing arms ( 12 ) fixed to side end portions ( 11   a ) of the cross-member ( 11 ) for articulated connection of the axle to the vehicle body and for support of the rear wheels. Each trailing arm ( 12 ) is formed by a pair of first, transversely inner half-shells ( 18, 19 ), that is, a front half-shell and a rear half-shell, respectively, securely connected to each other and to the respective end ( 11   a ) of the cross-member ( 11 ), and by a second transversely outer half-shell ( 20 ), securely connected to the pair of first half-shells ( 18, 19 ) so as to form therewith a structure having a closed cross-section.

This is a National Stage entry of International ApplicationPCT/EP2003/012337, with an international filing date of Nov. 5, 2003,which was published as Publication WO 2004/041561 A1, and the completedisclosure of which is incorporated into this application by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a twist-beam axle for the rearsuspension of a motor vehicle, as well as a method for the production ofsuch a twist-beam axle.

It is known in the automotive field the use of rear suspensions in whichthe two rear wheels are interconnected by means of a twist-beam axlecomprising basically a central cross-member compliant to torsion, whichextends substantially transversely and a pair of rigid trailing arms,attached to the ends of the cross-member, which support the rear wheelsand provide the articulation of the axle to the vehicle body.

According to the prior art, the trailing arms of the twist-beam axle areformed as elongated integral bodies, for example of tubular shape, whichare securely connected to the cross-member, for example by welding.Alternatively, a pair of trailing half-arms, that is, a front half-armand a rear half-arm, respectively, may be provided for instead of asingle trailing arm, wherein usually the rear half-arm is formed as asingle piece with the cross-member whereas the front one is fixed to thecross-member, for example by welding. These known arrangements, whichrequire a welded joint to be provided between the trailing arms, or thehalf-arms, and the cross-member, require a high dimensional and shapeprecision in the welding zones, in order to ensure the correct relativepositioning of the parts to be connected and the strength of the weldedconnection.

A twist-beam axle for the rear suspension of a motor vehicle, includinga central cross-member and a pair of trailing arms fixed to respectiveside end portions of the cross-member (11) is known from EP-A-0 743 205.According to this known solution, each trailing arm comprises a pair oftransversely inner half-shells, that is, a front half-shell and a rearhalf-shell, respectively, which are formed by prolongations of therespective end portion of the cross member, and a transversely outerhalf-shell securely connected to the pair of transversely innerhalf-shells so as to form therewith a structure having a closedcross-section.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide an improvedtwist-beam axle for the rear suspension of a motor vehicle with respectto the prior art, which is strong and easy to manufacture and whichenables the taking-up of possible plays in the zones of connectionbetween the trailing arms and the cross-member.

This object is fully achieved according to the invention by virtue of atwist-beam axle for the rear suspension of a motor vehicle having thecharacteristics defined in the first independent claim. According toanother aspect of the invention, this object is fully achieved by virtueof a method for the production of a twist-beam axle for the rearsuspension of a motor vehicle as defined in the second independentclaim.

In short, the invention is based on the idea of providing a twist-beamaxle in which each of the two trailing arms is comprised of a pair offirst, transversely inner half-shells, that is, a front half-shell and arear half-shell, respectively, securely connected to each other and tothe respective end of the cross-member by welding, and of a second,transversely outer half-shell, securely connected to the first twohalf-shells by welding so as to form therewith a rigid body having aclosed cross-section.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and the advantages of the invention will appear fromthe detailed description which follows, given purely by way ofnon-limiting example with reference to the appended drawings, in which:

FIGS. 1 and 2 are perspective views from above and from below,respectively, of a side end portion of a twist-beam axle according tothe invention;

FIG. 3 is an exploded perspective view of the portion of twist-beam axleshown in FIGS. 1 and 2;

FIG. 4 is a plan view from above of the portion of twist-beam axle shownin the preceding figures;

FIG. 5 is a section view along line V—V in FIG. 4 of the portion oftwist-beam axle shown in the preceding figures;

FIG. 6 is a section view along line VI—VI in FIG. 4 of the portion oftwist-beam axle shown in FIGS. 1 to 4;

FIG. 7 is a section view along line VII—VII in FIG. 4 of the portion oftwist-beam axle shown in FIGS. 1 to 4;

FIG. 8 is a section view along line VIII—VIII in FIG. 4 of the portionof twist-beam axle shown in FIGS. 1 to 4; and

FIG. 9 is a section view along line IX—IX in FIG. 4 of the portion oftwist-beam axle shown in FIGS. 1 to 4.

DETAILED DESCRIPTION OF THE INVENTION

In the description and the claims which follow, terms such as“longitudinal” and “transverse”, “inner” and “outer”, “front” and “rear”are to be understood as referred to the mounted condition on thevehicle.

Although only one of the two symmetric parts forming the structure ofthe twist-beam axle in question has been described and illustrated, forclear reasons of simplicity, it is clearly understood that thenon-described part is to be considered symmetric, or substantiallysymmetric, to that described.

By referring initially to FIGS. 1 to 4, a twist-beam axle for the rearsuspension of a motor vehicle is generally indicated 10 and comprises acentral cross-member 11 and a pair of trailing arms 12 fixed torespective side end portions 11 a of the cross-member (in the figuresonly the left-hand end is shown). A bush 13 for articulation of thetwist-beam axle 10 to the vehicle body is fixed to the front end of eachtrailing arm 12, whereas on a mounting structure 14 for a wheel-carrier(not shown) and a sheet plate 15 intended to provide a lower supportsurface for a spring (also, not shown) are fixed to the rear portion ofthe arm 12, on the transversely outer side and the transversely innerside, respectively.

The middle portion of the cross-member 11, indicated 11 b, has in itsvertical plane of symmetry a cross-section of predetermined shape, inthe illustrated example an omega-shape, adapted to provide thecross-member with the required elastic characteristics, in particularthe compliance to torsion. The end portions 11 a of the cross-member 11form each a head wall 11 c, downwardly inclined in the transversedirection, in which a hole 16 is provided for being passed through by atorsion bar 17 housed inside the middle portion 11 b of the cross-member11 and fixed at its ends to the trailing arms 12. Alternatively, thetorsion bar 17 may be fixed to the head walls 11 c of the side portions11 a of the cross-member, instead of being fixed to the trailing arms12. Moreover, the middle portion 11 b of the cross-member may assumeobviously any other suitable shape, either open (as in the illustratedexample) or closed.

According to the invention, each trailing arm 12 is comprised of threesheet metal parts 18, 19 and 20, formed as half-shells with open,essentially C-shaped cross-section, securely connected to each other,preferably by welding. These elements are a pair of transversely innerhalf-shells 18 and 19, that is, a front half-shell and a rearhalf-shell, respectively, intended to be fixed to the end portion 11 aof the cross-member 11, and a transversely outer half-shell 20, intendedto be fixed to the two inner half-shells 18, 19 so as to close thecross-section of the arm 12.

Each of the two inner half-shells 18, 19 comprises a first limb 18 a, 19a which extends essentially transversely and a second limb 18 b, 19 b,integral with the first one, which extends essentially longitudinally oris slightly inclined outwards relative to the longitudinal direction(FIG. 3).

Each first limb 18 a, 19 a is arranged to be welded both to therespective end portion 11 a of the cross-member, along a transverselyinner edge 21 suitably shaped to fit to the cross-member portion 11 a,and to the other first limb 19 a, 18 a, along a pair of transversestraight edges 22, 23 that is, an upper edge and a lower edge,respectively, arranged in use facing each other. Each second limb 18 b,19 b is arranged to be welded to the outer half-shell 20 along a pair oftransversely outer edges 24, 25 that is, an upper edge and a lower edge,respectively.

In order to enable to take up possible plays between the two innerhalf-shells 18, 19 and the cross-member portion 11 a, the twohalf-shells are shaped and dimensioned in such a manner that, when theyare arranged in their mounting position on to the cross-member, theirfacing edges 22, 23 are spaced apart by a certain gap, though verylittle, which is then filled by the welding bead which joins the twohalf-shells together along the edges 22, 23 during the assembling of theaxle.

Each transversely outer half-shell 20 has a substantially C-shapedcross-section, the upper and lower horizontal walls of which formtransversely inner edges 26 and 27, that is, an upper edge and a loweredge, respectively, for connection by welding to the transversely outeredges of the longitudinal limbs of the half-shells 18, 19. Where thetorsion bar 17 is fixed to the trailing arms 12, as in the illustratedembodiment, the vertical walls of the outer half-shells 20 haverespective holes 28 for engaging the ends of the bar 17.

As can be seen in the exploded view of FIG. 3 and in the section view ofFIG. 6, each rear inner half-shell 19 and each outer half-shell 20 haverespective through holes 29 and 30 into which a pin 31 is inserted forfixing the lower end of a damper (not shown).

As will be clear in the light of the preceding description, the methodof production of a twist-beam axle according to the invention providesfor, first of all, the manufacturing of the single parts of the axle,that is to say, the cross-member 11, the torsion bar 17 and thehalf-shells 18 to 20 intended to compose the trailing arms 12, and thenthe assembling of these parts by welding the pairs of inner half-shells18, 19 onto the cross-member 11 and the outer half-shells 20 onto thepairs of inner half-shells of the respective trailing arms.

Since the joining edges 21 to 27 of the half-shells 18 to 20 extendessentially in two dimensions, instead of three dimensions, the weldingoperations are easy to perform.

Naturally, the principle of the invention remaining unchanged,embodiments and manufacturing details may vary widely from thosedescribed and illustrated purely by way of non-limiting example.

1. Twist-beam axle for the rear suspension of a motor vehicle,comprising a central cross-member (11) and a pair of trailing arms (12)fixed to respective side end portions (11 a) of the cross-member (11),wherein each trailing arm (12) comprises a pair of front and reartransversely inner half-shells (18, 19) fixed to the respective side endportion (11 a) of the cross-member (11) and a transversely outerhalf-shell (20) securely connected to the transversely inner half-shells(18, 19) so as to form therewith a rigid body having a closedcross-section, characterised in that the transversely inner half-shells(18, 19) are separate components from the cross-member (11) and aresecurely connected to each other and to the respective side end portions(11 a) of the cross-member (11).
 2. Twist-beam axle according to claim1, characterised in that each of the transversely inner half-shells (18,19) comprises a first essentially transverse limb (18 a, 19 a) which issecurely connected to the respective side end portion (11 a) of thecross-member (11) and to the other transversely inner half-shell (19,18) of the same trailing arm (12), and a second essentially longitudinallimb (18 b, 19 b), integral with the first (18 a, 19 a), which issecurely connected to the transversely outer half-shell (20) of thetrailing arm (12).
 3. Twist-beam axle according to claim 2,characterised in that the first and second limbs (18 a, 18 b; 19 a, 19b) of the transversely inner half-shells (18, 19) and the transverselyouter half-shells (20) have, at least over part of their length, asubstantially C-shaped cross-section, the upper and lower horizontalwalls of which form respective first joining edges (22, 23; 24, 25; 26,27), facing two by two, for connection of the front and reartransversely inner half-shells (18, 19) to each other and to thetransversely outer half-shell (20).
 4. Twist-beam axle according toclaim 2, characterised in that the first limbs (18 a, 19 a) of each pairof transversely inner half-shells (18, 19) form, on the transverselyinner side, respective second joining edges (21) for connection of thesaid half-shells to the respective side end portion (11 a) of thecross-member (11).
 5. Twist-beam axle according to claim 1,characterised in that the half-shells (18, 19, 20) of each trailing arm(12) are securely connected to each other by welding and in that thetransversely inner half-shells (18, 19) of each trailing arm (12) aresecurely connected to the respective side end portion (11 a) of thecross-member (11) by welding.
 6. Twist-beam axle according to claim 3,characterised in that in the said first facing joining edges (22, 23)for connection of the front and rear transversely inner half-shells (18,19) to each other are spaced apart by a gap filled by a welding bead. 7.Twist-beam axle according to claim 1, characterised in that thecross-member (11) has, in its vertical plane of symmetry, anomega-shaped cross-section.
 8. Twist-beam axle according to claim 7,characterised in that the axle comprises also a torsion bar (17) housedinside the cross-member (11) and fixed at its ends to the transverselyouter half-shells (20) of the trailing arms (12).
 9. A method for theproduction of a twist-beam axle (10) for the rear suspension of a motorvehicle, comprising the steps of: a) providing a cross-member (11)having side end portions (11 a) adapted to engage a pair of trailingarms (12); b) providing, for each side end portion (11 a) of thecross-member (11), a pair of front and rear transversely innerhalf-shells (18, 19) adapted to be securely connected to each other andto the side end portion (11 a) of the cross-member (11), and atransversely outer half-shell (20) adapted to be securely connected tothe pair of transversely inner half-shells (18, 19) so as to formtherewith a rigid body of closed cross-section; c) securely connectingthe pairs of transversely inner half-shells (18, 19) onto the respectiveside end portions (11 a) of the cross-member (11); d) securelyconnecting the transversely outer half-shells (20) onto the respectivepairs of transversely inner half-shells (18, 19).
 10. Method accordingto claim 9, characterised in that the step b) comprises the operation offorming both the front and rear transversely inner half-shells (18, 19)in such a way that they comprise each a first essentially transverselimb (18 a, 19 a) adapted to be securely connected to the respectiveside end portion (11 a) of the cross-member (11) and to the othertransversely inner half-shell (19, 18) of the same trailing arm (12),and a second essentially longitudinal limb (18 b, 19 b), integral withthe first (18 a, 19 a), adapted to be securely connected to thetransversely outer half-shell (20) of the trailing arm (12), wherein thesaid first and second limbs (18 a, 18 b; 19 a, 19 b) of each pair oftransversely inner half-shells (18, 19) and each transversely outerhalf-shell (20) have, at least over part of their length, asubstantially C-shaped cross-section, the upper and lower horizontalwalls of which form respective first joining edges (22, 23; 24, 25; 26,27), adapted to be disposed facing two by two for connection of thefront and rear transversely inner half-shells (18, 19) to each other andto the transversely outer half-shell (20), and wherein the first limbs(18 a, 19 a) of each pair of transversely inner half-shells (18, 19)form, on the transversely inner side, respective second joining edges(21) for connection of the transversely inner half-shells to therespective side end portion (11 a) of the cross-member (11).
 11. Methodaccording to claim 10, characterised in that the steps c) and d)comprise the operation of welding the said first and second joiningedges (22, 23; 24, 25; 26, 27; 21).